1. Field of the Invention
The present invention relates to an aluminum alloy and, more particularly, to an aluminum alloy in which changes in thermal conductivity depending on temperature are improved.
2. Description of the Related Art
Typically, engines are capable of exhibiting maximum performance when maintaining a predetermined temperature or higher. Thus, engine parts should possess low thermal conductivity so as to prevent internal heat of a combustion chamber from being emitted to the outside under the low temperature conditions immediately after starting the engine. Furthermore, high thermal conductivity is required to prevent overheating of the combustion chamber under the high temperature conditions at which the temperature of the combustion chamber is elevated after a predetermined period of time following starting the engine.
When the temperature of the combustion chamber is elevated to a predetermined level or higher, problems such as knocking, overheating and adhesion may occur. With the goal of overcoming such problems, it is required that heat dissipation performance, namely, thermal conductivity is superior.
Since a conventional aluminum alloy for use in engine cylinder heads has high thermal conductivity at room temperature and low thermal conductivity at high temperature, engine efficiency may be reduced, undesirably deteriorating fuel efficiency.
FIG. 1 is a graph illustrating thermal conductivity, depending on the temperature, of a conventional AC2B gravity cast aluminum alloy thermally treated under T7 conditions. A typical AC2B alloy is composed of 2˜4 wt % of copper (Cu), 5˜7 wt % of silicon (Si), 0.5 wt % or less of magnesium (Mg), 1 wt % or less of zinc (Zn), 0.8 wt % or less of iron (Fe), 0.50 wt % or less of manganese (Mn), 0.35 wt % or less of nickel (Ni), 0.20 wt % or less of titanium (Ti), 0.20 wt % or less of lead (Pb), 0.10 wt % or less of tin (Sn), 0.20 wt % or less of chromium (Cr), and the remainder of aluminum (Al).
As illustrated in FIG. 1, an AC2B aluminum alloy has a thermal conductivity of 185 W/m*K or more at room temperature (25° C.) and a thermal conductivity of 185 W/m*K or less at high temperature (200° C.). The AC2B alloy in which thermal conductivity decreases in proportion to an increase in the temperature is undesirable in terms of preheating at room temperature and also in terms of heat dissipation at high temperature. Hence, there is a need for a novel aluminum alloy having low thermal conductivity at room temperature and high thermal conductivity at high temperature.